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222-9+11+12:2*14+14 = ? ( )

Toán Lớp 7: 1/10.11.12+1/11.12.13+-+1/27.28.29+1/28.29.30 tính

Toán Lớp 7: 1/10.11.12+1/11.12.13+….+1/27.28.29+1/28.29.30 tính

Comments ( 2 )

  1. Giải đáp:
     19/4785
    Lời giải và giải thích chi tiết:
    \frac{1}{10.11.12}+\frac{1}{11.12.13}+….+\frac{1}{27.28.29}+\frac{1}{28.29.30}
    =1/2 . ( 1/10.11 – 1/11.12 + 1/11.12-1/12.13+…+1/27.28 – 1/28.29+1/28.29 – 1/29.30)
    =1/2 . (1/10.11 – 1/29.30 ) 
    =1/2 . (1/110 – 1/870)
    =1/2 . 38/4785
    =19/4785

  2. \frac{1}{10.11.12}+\frac{1}{11.12.13}+….+\frac{1}{27.28.29}+\frac{1}{28.29.30}
    =1/2 . ( 1/10.11 – 1/11.12 + 1/11.12-1/12.13+…+1/27.28 – 1/28.29+1/28.29 – 1/29.30)
    =1/2 . (1/10.11 – 1/29.30 ) 
    =1/2 . (1/110 – 1/870)
    =1/2 . 38/4785
    =19/4785

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222-9+11+12:2*14+14 = ? ( )